The invention relates to a method of controlling a display device having a back light, as well as to such a display device. In particular, this invention relates to such a method and a device mounted to a programmable controller.
A back light is generally provided to a display device for a PLC or a so-called programmable terminal (PT) for improving the visibility of data and character arrays which are displayed on the display device.
On the other hand, programmable controllers for controlling apparatus of different kinds are being required not only to be usable for a wider variety of purposes but also to be compact. Thus, display devices having a back light are coming to be mounted to a programmable controller. Back lights which are mounted to a conventional programmable controller, however, are controlled to be switched on and off by a system program according to a preliminarily set on/off pattern. As a result, most of the controls were either for leaving it on all the time or for keeping the light on for a specified length t whenever a button is pressed, as shown in FIG. 7.
A back light for a display device is not only for improving the visibility of data and character arrays which are displayed on the display device but also to serve to give a warning to the user. Thus, it is desirable that its on-off control be effected automatically, in the case of a programmable controller, for example, according to conditions of different kinds set by the user for providing a warning. With a back light for a conventional display device, however, such a flexible on-off control suitable to the user's purpose for use could not be effected because its on-off control was uniquely determined by a system program.